In every Animal Crossing game there is a rock in each town that gives out money when hit it with a shovel or axe. It only does this once per day but you can get up to 8,000 bells if you hit it enough. Every day there will be an extra rock in your town. Hit it with a shovel and it will break and reveal a different mineral. You can take these to Cyrus (once he wakes up) and use them as an additional way to make your furniture different. You can also just sell them. Once you have the silver shovel, you have a chance of making gems come out of the money rock instead of bells. Also, you can take 3 gold gems to Cyrus and he'll make you a random piece of a special gold furniture set.